For words that have only 3 letters, there is absolutely no 4th letter. One example is with the word “incorporate”, there are no extra letters afterwards and thus should be the word "insert". The word “addict” is in the BIP39 wordlist however, you would have applied “addi” for “addict”. To https://freshbookmarking.com/story18824827/top-guidelines-of-bip39-word-list-pdf